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Cerium-Catalyzed C–H Functionalizations of Alkanes Utilizing Alcohols as Hydrogen Atom Transfer Agents
journal contribution
posted on 2020-03-23, 19:47 authored by Qing An, Ziyu Wang, Yuegang Chen, Xin Wang, Kaining Zhang, Hui Pan, Weimin Liu, Zhiwei ZuoModern
photoredox catalysis has traditionally relied upon metal-to-ligand
charge-transfer (MLCT) excitation of metal polypyridyl complexes for
the utilization of light energy for the activation of organic substrates.
Here, we demonstrate the catalytic application of ligand-to-metal
charge-transfer (LMCT) excitation of cerium alkoxide complexes for
the facile activation of alkanes utilizing abundant and inexpensive
cerium trichloride as the catalyst. As demonstrated by cerium-catalyzed
C–H amination and the alkylation of hydrocarbons, this reaction
manifold has enabled the facile use of abundant alcohols as practical
and selective hydrogen atom transfer (HAT) agents via the direct access
of energetically challenging alkoxy radicals. Furthermore, the LMCT
excitation event has been investigated through a series of spectroscopic
experiments, revealing a rapid bond homolysis process and an effective
production of alkoxy radicals, collectively ruling out the LMCT/homolysis
event as the rate-determining step of this C–H functionalization.